U.S. patent number 8,784,625 [Application Number 12/737,158] was granted by the patent office on 2014-07-22 for sensor element containing a sealing element for a functional component.
This patent grant is currently assigned to Robert Bosch GmbH. The grantee listed for this patent is Alexander Bluthard, Ulrich Eisele, Uwe Glanz, Benjamin Hagemann, Petra Kuschel, Gudrun Oehler, Steffen Polster, Jochen Rager, Georg Rixecker, Frank Schnell, Thomas Wahl. Invention is credited to Alexander Bluthard, Ulrich Eisele, Uwe Glanz, Benjamin Hagemann, Petra Kuschel, Gudrun Oehler, Steffen Polster, Jochen Rager, Georg Rixecker, Frank Schnell, Thomas Wahl.
United States Patent |
8,784,625 |
Wahl , et al. |
July 22, 2014 |
Sensor element containing a sealing element for a functional
component
Abstract
A sensor element having a layered construction and configured to
detect a physical property of a gas or a liquid includes a
functional component situated in the interior, which functional
component is connected electrically to a conductor element, which
conductor element extends up to the outer surface or up into the
surroundings of the sensor element. The sensor element has at least
one sealing element which adjoins the functional component and/or
the conductor element. The conductor element and the at least one
sealing element are configured to be gas-tight at least regionally
in the interior of the sensor element and are situated in such a
way that the functional component is separated gas-tight from the
surroundings of the sensor element.
Inventors: |
Wahl; Thomas (Pforzheim,
DE), Rixecker; Georg (Leinfelden-Echterdingen,
DE), Polster; Steffen (Stuttgart, DE),
Glanz; Uwe (Asperg, DE), Oehler; Gudrun
(Stuttgart, DE), Eisele; Ulrich (Stuttgart,
DE), Hagemann; Benjamin (Gerlingen, DE),
Bluthard; Alexander (Stuttgart, DE), Schnell;
Frank (Kornwestheim, DE), Rager; Jochen
(Bisingen, DE), Kuschel; Petra (Leonberg-Hoefingen,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Wahl; Thomas
Rixecker; Georg
Polster; Steffen
Glanz; Uwe
Oehler; Gudrun
Eisele; Ulrich
Hagemann; Benjamin
Bluthard; Alexander
Schnell; Frank
Rager; Jochen
Kuschel; Petra |
Pforzheim
Leinfelden-Echterdingen
Stuttgart
Asperg
Stuttgart
Stuttgart
Gerlingen
Stuttgart
Kornwestheim
Bisingen
Leonberg-Hoefingen |
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A |
DE
DE
DE
DE
DE
DE
DE
DE
DE
DE
DE |
|
|
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
|
Family
ID: |
40847883 |
Appl.
No.: |
12/737,158 |
Filed: |
April 24, 2009 |
PCT
Filed: |
April 24, 2009 |
PCT No.: |
PCT/EP2009/054955 |
371(c)(1),(2),(4) Date: |
March 24, 2011 |
PCT
Pub. No.: |
WO2009/153092 |
PCT
Pub. Date: |
December 23, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110162436 A1 |
Jul 7, 2011 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 16, 2008 [DE] |
|
|
10 2008 002 446 |
|
Current U.S.
Class: |
204/426 |
Current CPC
Class: |
G01N
27/4071 (20130101); G01N 27/4077 (20130101); G01N
27/4067 (20130101) |
Current International
Class: |
G01N
27/26 (20060101) |
Field of
Search: |
;204/425,426
;73/23.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1288649 |
|
Mar 2001 |
|
CN |
|
198 51 966 |
|
May 2000 |
|
DE |
|
10 2004 025 949 |
|
Dec 2005 |
|
DE |
|
2 316 178 |
|
Feb 1998 |
|
GB |
|
2005-33809 |
|
Feb 2005 |
|
JP |
|
Primary Examiner: Caputo; Lisa
Assistant Examiner: Roy; Punam
Attorney, Agent or Firm: Kenyon & Kenyon LLP
Claims
What is claimed is:
1. A sensor element for detecting one of a concentration of a gas
component or a temperature of an exhaust gas of an internal
combustion engine, comprising: a functional component situated in
interior portion of the sensor element and between a first ceramic
layer and a second ceramic layer; a conductor element, wherein the
functional component is connected electrically conductive to the
conductor element, and wherein the conductor element extends one of
(i) up to an outer surface of the sensor element or (ii) up into
surroundings of the sensor element, and wherein at least a portion
of the conductor element extends at least partially within the same
layer plane as the functional component and is gas-tight; and at
least one sealing element adjoining at least one of the functional
component and the conductor element, wherein at least a portion of
the sealing element is situated at least partially within the same
layer plane as a layer at least partially enclosing the functional
component and is gas-tight; wherein the conductor element and the
at least one sealing element are (i) configured to be gas-tight at
least regionally in the interior of the sensor element and (ii)
situated in such a way that the functional component is separated
in a gas-tight manner from the surroundings of the sensor element,
and (iii) are at least partially situated and gas-tight between the
first and the second ceramic layers and (iv) positioned in such a
way that the functional component is separated gas-tight from the
surroundings of the sensor element, and wherein the sensor element
has a layered construction.
2. The sensor element as recited in claim 1, wherein the functional
component is at least one of an electrical resistance heater and a
supply line to an electrical resistance heater.
3. The sensor element as recited in claim 1, wherein the functional
component contains a material which oxidizes in the presence of
oxygen at a temperature of 650.degree. C., the material being at
least 50 percent of the functional component by weight.
4. The sensor element as recited in claim 1, wherein the functional
component includes one of a noble metal, a base metal, or a carbon
nanotube, wherein the one of the noble metal, the base metal, or
the carbon nanotube is at least 50 percent of the functional
component by weight.
5. The sensor element as recited in claim 1, wherein the gas-tight
region of the conductor element has at least one of: (i) a closed
porosity; (ii) an alloy element having one of gold or silver; (iii)
a glass phase; and (iv) a glass-ceramic phase.
6. The sensor element as recited in claim 1, wherein the sensor
element has a feed-through extending from the outer surface of the
sensor element through at least one ceramic layer up to the plane
of the functional component, and wherein at least one of the
sealing element and the conductor element is at least partially
situated inside the feed-through and gas-tight in a region inside
the feed-through.
7. The sensor element as recited in claim 6, wherein the sealing
element is situated on the inner side of the feed-through.
8. A sensor element for detecting one of a concentration of a gas
component or a temperature of an exhaust gas of an internal
combustion engine, comprising: a functional component situated in
interior portion of the sensor element; a conductor element,
wherein the functional component is connected electrically
conductive to the conductor element, and wherein the conductor
element extends one of (i) up to an outer surface of the sensor
element or (ii) up into surroundings of the sensor element; and at
least one sealing element adjoining at least one of the functional
component and the conductor element, wherein: the conductor element
and the at least one sealing element are (i) configured to be
gas-tight at least regionally in the interior of the sensor element
and (ii) situated in such a way that the functional component is
separated in a gas-tight manner from the surroundings of the sensor
element, and wherein the sensor element has a layered construction,
the functional component is situated between a first ceramic layer
and a second ceramic layer; the conductor element and the at least
one sealing element are at least partially situated and gas-tight
between the first and the second ceramic layers, the conductor
element and the at least one sealing element are positioned in such
a way that the functional component is separated gas-tight from the
surroundings of the sensor element, the sensor element has a
feed-through extending from the outer surface of the sensor element
through at least one ceramic layer up to the plane of the
functional component, and at least one of the sealing element and
the conductor element is at least partially situated inside the
feed-through and gas-tight in a region inside the feed-through,
wherein the sealing element has a cavity, and wherein at least a
part of the conductor element is situated in the interior of the
cavity.
9. A sensor element for detecting one of a concentration of a gas
component or a temperature of an exhaust gas of an internal
combustion engine, comprising: a functional component situated in
interior portion of the sensor element; a conductor element,
wherein the functional component is connected electrically
conductive to the conductor element, and wherein the conductor
element extends one of (i) up to an outer surface of the sensor
element or (ii) up into surroundings of the sensor element; and at
least one sealing element adjoining at least one of the functional
component and the conductor element, wherein: the conductor element
and the at least one sealing element are (i) configured to be
gas-tight at least regionally in the interior of the sensor element
and (ii) situated in such a way that the functional component is
separated in a gas-tight manner from the surroundings of the sensor
element, and wherein the sensor element has a layered construction,
the functional component is situated between a first ceramic layer
and a second ceramic layer; the conductor element and the at least
one sealing element are at least partially situated and gas-tight
between the first and the second ceramic layers, the conductor
element and the at least one sealing element are positioned in such
a way that the functional component is separated gas-tight from the
surroundings of the sensor element, the sensor element has a
feed-through extending from the outer surface of the sensor element
through at least one ceramic layer up to the plane of the
functional component, and at least one of the sealing element and
the conductor element is at least partially situated inside the
feed-through and gas-tight in a region inside the feed-through,
wherein the conductor element has a cavity, and wherein at least a
part of the sealing element is situated in the interior of the
cavity.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a sensor element containing a
sealing element for a functional component.
2. Description of Related Art
A sensor element having a layered construction is known, for
example, from published German patent application document DE 10
2004 025 949 A1, and has a printed conductor, which extends from an
outer side of the sensor element through a feedthrough up into the
interior of the sensor element. A cover layer is situated in the
area of the feedthrough in such a way that a gas located outside
the sensor element may only reach the interior of the sensor
element via a diffusion path, which at least regionally runs
parallel to the outer surface of the sensor element. A sensor
element constructed in this way has the advantage that contaminants
do not accumulate or only accumulate substantially less in the
interior of the sensor element.
Such a sensor element has the disadvantage that access of a gas
which is located outside the sensor element, in particular an
oxygenated exhaust gas or ambient air, to the functional component,
which is situated in the interior of the sensor element, is
possible, which results there in oxidative processes in particular
at high temperatures, which may impair the function of the sensor
element and contribute to premature aging and to the failure of the
sensor element. These problems occur more extensively the baser and
thus more reactive the material of the functional component. On the
other hand, the use of such materials is attractive for cost
reasons.
BRIEF SUMMARY OF THE INVENTION
The sensor element according to the present invention has the
advantage over the related art in that an access of a gas, which is
located outside the sensor element, to the functional component is
not possible, and therefore oxidation of the functional component
may be prevented even at high temperatures and while employing base
materials. For this purpose, the conductor element and the sealing
element in the interior of the sensor element are at least
regionally designed as gas-tight and are situated in such a way
that the functional component is separated gas-tight from the
surroundings of the sensor element.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross-sectional view of an end section of an example
embodiment of a sensor according to the present invention.
FIG. 2 shows a cross-sectional view of an end section of another
example embodiment of a sensor according to the present
invention.
FIGS. 3 and 3a show a cross-sectional view of an end section of
another example embodiment of a sensor according to the present
invention.
FIG. 4 shows a cross-sectional view of an end section of another
example embodiment of a sensor according to the present
invention.
FIG. 5 shows a cross-sectional view of an end section of another
example embodiment of a sensor according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
As a first exemplary embodiment of the present invention, FIG. 1
shows a connection-side end section of a sensor element 20, which
is situated in a housing of a gas sensor (not shown) and is used,
for example, for determining the oxygen concentration in an exhaust
gas of an internal combustion engine (not shown) or the temperature
of the exhaust gas.
Sensor element 20 is constructed from ceramic layers 21, 22, 28,
29, of which two are formed as a first and a second solid
electrolyte film 21, 22 and contain yttrium-oxide-stabilized
zirconium oxide (YSZ) and two are formed as an outer and an inner
printed, electrically insulating layer 28, 29 and contain aluminum
oxide.
First and second solid electrolyte films 21, 22 are located above
and below inner printed electrically insulating layer 29. Outer
printed electrically insulating layer 28 is situated above second
solid electrolyte film 22. Of course, the sensor element may have
further layers for implementing functionalities of sensor element
20 which are known per se. These further layers may be made of
ceramic material, for example.
A functional component 31, which is composed of an electrical
resistance heater and a supply line 131 to the electrical
resistance heater, is located inside inner printed electrically
insulating layer 29. The electrical resistance heater causes,
together with external wiring (not shown), the heating of sensor
element 20 to temperatures up to significantly greater than
650.degree. C. Supply line 131 to the electrical resistance heater
extends up to the connection-side end section of sensor element 20,
while the electrical resistance heater is situated in the
diametrically opposing, measurement-side end section of sensor
element 20 (not shown in FIG. 1). The material of which functional
component 31 is made in this example has a high palladium
proportion, for example, a proportion of greater than 50 percent by
weight. Alternatively, other materials which also oxidize at
temperatures greater than 650.degree. C. in the presence of oxygen
come into consideration.
Since the material, of which functional component 31 is made in
this example, oxidizes at the operating temperatures of functional
component 31 of greater than 650.degree. C. in the presence of
oxygen, it is provided that functional component 31 is separated
gas-tight from surroundings 500 of sensor element 20.
In the area of the connection-side end section, sensor element 20
has a feedthrough 51 which extends, starting from functional
component 31, through parts of inner printed electrically
insulating layer 29, through second solid electrolyte film 22, and
through outer printed electrically insulating layer 28 up to outer
surface 100 of sensor element 20. The feedthrough has the form of a
circular cylinder having a diameter of 0.3 mm to 1.5 mm, preferably
0.5 mm to 1.2 mm, whose axis is perpendicular to layers 21, 22, 28,
29. Of course, it would also be possible to give the footprint of
feedthrough 51 an oval or polygonal shape and/or to situate
feedthrough 51 at a different angle to layers 21, 22, 28, 29. A
gas-tight, electrical insulation 61, which contains aluminum oxide,
aluminum-magnesium spinel, or forsterite, for example, and has a
thickness of 2 .mu.m-100 .mu.m, preferably 5 .mu.m-50 .mu.m, is
applied to the wall of feedthrough 51, which is in the form of a
cylindrical jacket. Insulation 61 thus has the form of a hollow
cylinder.
A conductor element 41 is connected electrically conductive to
functional component 31 in feedthrough 51 and in the interior of
the hollow cylinder which is formed by insulation 61 with the aid
of a conductive fixing attachment 75, an electrically conductive
and mechanically fixing compound. Conductor element 41 is a
platinum wire 141, which extends inside feedthrough 51 along its
axis and up into surroundings 500 of sensor element 20. Platinum
wire 141 has a diameter of 50 .mu.m-250 .mu.m and has a gas-tight
design. The remaining space of feedthrough 51, i.e., the space in
the interior of the hollow cylinder formed by insulation 61, which
is not occupied by conductive fixing attachment 75 or by platinum
wire 141, is filled up by a sealing element 71, which is made of a
gas-tight and electrically insulating glass or glass-ceramic
compound 171. Glass or glass-ceramic compound 171 is
SiO.sub.2-based or phosphate-based having further proportions of
Al.sub.2O.sub.3, MgO, CaO, and/or B.sub.2O.sub.3. Furthermore,
glass or glass-ceramic compound 171 may contain proportions of ZnO,
SrO, BaO, La.sub.2O.sub.3, TiO.sub.2, and Na.sub.2O totaling less
than 50 percent by weight, preferably less than 10 percent by
weight. The coefficient of thermal expansion of employed glass or
glass-ceramic compound 171 is between 4.5*10.sup.-6/K and
12*10.sup.-6/K for reasons of adaptation to the thermal expansion
of the surrounding ceramics.
Thick-layer processes which are known per se are used for producing
sensor element 20 according to the first exemplary embodiment, for
example, screen printing, transfer printing, and through suction
processes. Glass or glass-ceramic compound 171 is dispensed,
prepared in powdered form, which is unpressed or pressed into
shape, or in paste form, into feedthrough 51 and fired using a
subsequent heating process, glass or glass-ceramic compound 171
becoming gas-tight through fusion and subsequent solidification.
The firing temperature of the employed glasses is in the range from
900.degree. C.-1400.degree. C. The fired glass or the fired glass
ceramic is high-temperature resistant and has a glass transition
point of greater than 750.degree. C.
FIG. 2 shows a second exemplary embodiment of the present
invention, which differs from the first exemplary embodiment in
that conductor element 41 is designed as a metal core 241. Metal
core 241 has the form of a circular cylinder having a diameter of
80 .mu.m-400 .mu.m and terminates flatly with outer surface 100 of
sensor element 20, like sealing element 71. Metal core 241 is
connected mechanically and electrically conductive with the aid of
a conductive fixing attachment 75 to functional component 31, as in
the first exemplary embodiment of platinum wire 141, or a ductile
metal layer 275 made of gold or nickel, which is 10 .mu.m-200 .mu.m
thick, is located between metal core 241 and functional component
31. Metal core 241 contains platinum or nickel or is made of a
chromium-nickel steel and has a gas-tight design.
A planar contact element 42, which is connected mechanically and
electrically conductive to metal core 241, and is used for
contacting the sensor element with an analysis and/or supply unit
(not shown), is situated on outer surface 100 of sensor element
20.
FIGS. 3 and 3a show a third exemplary embodiment of the present
invention, which differs from the second exemplary embodiment in
that contact element 42 is not only situated on outer surface 100
of sensor element 20, but rather also protruding into feedthrough
51 and into the interior of the hollow cylinder formed by
insulation 61. Insulation 61 is composed and positioned as in the
preceding examples, and is gas-tight in particular and takes over
the function of sealing element 71 in this exemplary embodiment.
Conductor element 41 includes a gas-tight, conductive filling 341
in this exemplary embodiment, which is connected electrically
conductive to contact element 42 and to functional component 31.
Gas-tight, conductive filling 341 fills up the entire cross-section
of feedthrough 51, together with insulation 61, below the
protrusion of contact element 42. Gas-tight, conductive filling 341
is made of a material which contains 5-90 percent by volume,
preferably 10-50 percent by volume, platinum or platinum group
metals (nickel, palladium, platinum) and also a glass or glass
ceramic phase, whose composition corresponds to the composition of
glass or glass ceramic compound 171 of the first exemplary
embodiment, for example, and optionally contains alloy elements
having a low sintering point, such as gold or silver. Filling 341
has a closed porosity.
In FIG. 3a, dimension a is the diameter of the hollow cylinder
formed by insulation 61, dimension b is the length of the
protrusion of contact element 42 into the interior of the hollow
cylinder formed by insulation 61, dimension c is the width of this
protrusion, dimension d is the thickness of layer 28, dimension e
is the thickness of layer 29, and dimension f is the length of the
protrusion of contact element 42 into gas-tight, conductive filling
341. Dimensions a, b, c, d, e, and f are selected as follows: a=900
.mu.m, b=190 .mu.m, c=30 .mu.m, d=25 .mu.m, e=45 .mu.m, and f=135
.mu.m. Alternatively, the dimensions are selected within the
following limits: 300 .mu.m<a<1500 .mu.m, 20
.mu.m<b<300 .mu.m, 2 .mu.m<c<100 .mu.m, 5
.mu.m<d<50 .mu.m, 5 .mu.m<e<70 .mu.m, 20
.mu.m<f<300 .mu.m, preferably: 500 .mu.m<a<1200 .mu.m,
100 .mu.m<b<200 .mu.m, 5 .mu.m<c<50 .mu.m, 20
.mu.m<d<30 .mu.m, 40 .mu.m<e<50 .mu.m, 50
.mu.m<f<200 .mu.m.
FIG. 4 shows a fourth exemplary embodiment of the present
invention, which differs from the third exemplary embodiment in
that the protrusion of contact element 42 extends up to the base of
feedthrough 51 and is connected electrically conductive there to
functional component 31. The protrusion of contact element 42 has a
gas-tight design and takes over the function of conductor element
41 in this exemplary embodiment and is designed as a hollow
cylinder. The interior of the protrusion of contact element 42 is
filled up by sealing element 71, which is made up of a glass or
glass-ceramic compound 471 in this example. The composition of
glass or glass-ceramic compound 471 corresponds to the composition
of glass or glass-ceramic compound 171 from the first exemplary
embodiment. The part of contact element 42 which is situated on
outer surface 100 has a thickness of 2 .mu.m-100 .mu.m, preferably
5 .mu.m-25 .mu.m in this exemplary embodiment.
In an alternative specific embodiment of exemplary embodiments 1
through 4, layer 22 is made up of a gas-tight, electrically
insulating material, which predominantly contains aluminum oxide
and has a closed porosity, for example. Layer 22 takes over the
function of sealing element 71 in this variant and conductor
element 41 may be led through layer 22 in direct contact therewith.
Insulation 61 may be dispensed with in this case.
The gas-tight separation of functional component 31 from
surroundings 500 of sensor element 20 may also take place in that
conductor element 41 runs at least partially within the same layer
plane as functional component 31 and is gas-tight there, and
sealing element 71 is situated at least partially within the same
layer plane as a layer 29, which encloses functional component 31,
and is gas-tight there. It is advantageously possible in this case
to achieve a gas-tight separation of functional component 31 from
surroundings 500 of sensor element 20 without a feedthrough 51
through sensor element 20 which is used for contacting functional
component 31, having to be gas-tight. The fifth exemplary
embodiment of the present invention, which is based on this idea,
is shown in FIG. 5.
FIG. 5 shows a connection-side end section of a sensor element 20,
which is situated in a housing of a gas sensor (not shown) and is
used, for example, for determining the oxygen concentration in an
exhaust gas of an internal combustion engine (not shown) or the
temperature of the exhaust gas.
Sensor element 20 is constructed from ceramic layers 21, 22, 28,
29, of which two are designed as a first and a second solid
electrolyte film 21, 22 and contain yttrium-oxide-stabilized
zirconium oxide (YSZ) and two are designed as an outer and an inner
printed, electrically insulating layer 28, 29 and contain aluminum
oxide.
First and second solid electrolyte films 21, 22 are located above
and below inner printed electrically insulating layer 29. Outer
printed electrically insulating layer 28 is situated above second
solid electrolyte film 22.
A functional component 31, which is composed of an electrical
resistance heater and a supply line 131 to the electrical
resistance heater, is located inside inner printed electrically
insulating layer 29. The electrical resistance heater causes,
together with an external wiring (not shown), the heating of sensor
element 20 to temperatures greater than 650.degree. C. Supply line
131 to the electrical resistance heater extends at least close to
the connection-side end section of sensor element 20, while the
electrical resistance heater is situated in the diametrically
opposing, measurement-side end section of sensor element 20 (not
shown in FIG. 5). The material of which functional component 31 is
made of in this example has a high palladium proportion, for
example, a proportion of greater than 50 percent by weight.
In the area of its connection-side end section, sensor element 20
has a feedthrough 51, which extends from the layer plane in which
functional component 31 is located up to outer surface 100 of
sensor element 20. A gas-tight, electrical insulation 61 is applied
to the wall of feedthrough 51, in the form of a cylindrical
sheath.
A contact element 42 extends from outer surface 100 of sensor
element 20 along the inner side of insulation 61 up to the layer
plane in which functional component 31 lies. Contact element 42 is
designed as a hollow cylinder inside feedthrough 51 with an
interior remaining free. Contact element 42 is connected
electrically conductive to functional component 31.
Since the material of which functional component 31 is made of
oxidizes in the presence of oxygen at operating temperatures of
functional component 31 of greater than 650.degree. C., functional
component 31 is separated gas-tight from surroundings 500 of sensor
element 20.
For this purpose, a part 29a of inner electrically insulating
printed layer 29 is gas-tight in an area situated laterally around
feedthrough 51. This part 29a of inner electrically insulating
printed layer 29 takes over the function of sealing element 71.
Furthermore, a gas-tight supply line 31a, preferably having high
platinum content, which electrically connects contact element 42
and functional component 31 to one another, is located in the layer
plane of functional component 31. This gas-tight supply line 31a
takes over the function of conductor element 41. The gas-tightness
of sealing element 71 and conductor element 41 is achieved by a
closed porosity or by sintering additives of a glass or
glass-ceramic phase or by adding alloy elements which sinter at low
temperatures, such as gold or silver.
The area which is situated laterally around feedthrough 51 extends,
starting from the outer edge of feedthrough 51, to a width of
between 300 .mu.m and 5000 .mu.m. In one specific embodiment it may
also be provided that functional component 31 and gas-tight supply
line 31a overlap on a length of up to 1 mm.
All exemplary embodiments allow the use of a material which
oxidizes under the influence of oxygen for functional component 31
at operating temperatures of up to greater than 650.degree. C. This
material may be a relatively cost-effective noble metal in
comparison to platinum, such as palladium or gold. Furthermore, the
use of metals which are not noble metals is possible, such as
nickel, tungsten, molybdenum, titanium, tantalum, niobium, iron, or
chromium. For this purpose, it is to be noted that if these
materials are used, oxidations of the materials used for the
functional components are also to be prevented during the
manufacturing process. For this purpose, in particular during the
sintering procedure, the use of a reducing atmosphere is
advantageous, in particular the gases argon and nitrogen having a
volume proportion of up to 5% hydrogen.
If materials are used for functional component 31 which react with
aluminum oxide, for example, various metals (atomic type Me) do
this, in that they react to form MeAl.sub.2O.sub.4 (spinel) at high
temperatures, direct contact between functional component 31 and
aluminum oxide is to be prevented, for example, by providing a
diffusion barrier layer. In the case of nickel, it may be made of
zirconium oxide, for example. Since the coefficient of thermal
expansion of the relevant materials sometimes significantly
deviates from the coefficient of thermal expansion of the employed
ceramics, it may be advantageous for the material of which
functional component 31 is made of to have a ceramic second phase
(cermet), whereby it is possible to bring the coefficients of
thermal expansion into harmony.
A further possibility is the use of carbon in the form of carbon
nanotubes as the material for functional component 31. The material
containing the carbon nanotubes is advantageously processed as a
paste for this purpose, for example, with the aid of
screenprinting. A debinding of this paste may be performed in an
oxygenated atmosphere, the sintering process is to be performed in
a protective gas atmosphere. Since material containing carbon
nanotubes having a high specific conductance is presently only
available to a limited extent, it may be advantageous to use
materials in functional components 31 which have carbon in the form
of carbon nanotubes (for example, as a heating resistor of an
electrical heater) in addition to other materials (for example,
having platinum in the supply lines of this heater). If the heating
resistor of an electrical heater is constructed by carbon in the
form of carbon nanotubes, the possibility exists of designing this
heating resistor as planar, for example, in an area whose edge
lengths are greater than 2 mm.
* * * * *